题目描述

十进制20位数据乘法

输入描述：

两个不超过20位都不为0的十进制字符串

输出描述：

字符串相乘结果

示例1

输入

20000000000000000000
30000000000000000000

输出

600000000000000000000000000000000000000

Python代码

# -*- coding:utf-8 -*-

def recursive_multiply(x, y, n):
    if n==1:
        return x*y
    else:
        a = x/pow(10, n/2)
        b = x-a*pow(10, n/2)
        c = y/pow(10, n/2)
        d = y-c*pow(10, n/2)

    ac = recursive_multiply(a, c, n/2)
    bd = recursive_multiply(b, d, n/2)
    p = recursive_multiply(a+b, c+d, n/2) - ac -bd

    return ac*pow(10, n) + p*pow(10, n/2) + bd

if __name__ == '__main__':
    num1 = int(raw_input())
    num2 = int(raw_input())
    r = recursive_multiply(num1,num2,4)
    print r